Thank you @TikiTech and @silverD ! That the problem could be the circuit breaker actually makes sense. I do not have access to the robot now, but I will test it tomorrow. As described in another thread (https://www.chiefdelphi.com/t/pdp-makes-clicking-sound-every-1-2-seconds-when-a-victor-spx-is-connected/342482?u=roborb) I believe we had a bad 40-amp breaker that found its way onto this robot. I should have discorded that breaker.